This invention relates generally to an exposure apparatus such as a semiconductor exposure apparatus and, more particularly, to a scanning stage device suitably usable in a scanning type exposure apparatus wherein an arcuate or rectangular slit-like region of a pattern of a reticle is imaged on a substrate such as a wafer and wherein both the reticle and the substrate are scanningly moved so that the reticle pattern as a whole is exposed and transferred to the substrate.
In a scanning type exposure apparatus wherein both a reticle (original) and a substrate are scanningly moved so that a reticle pattern as a whole is transferred onto the substrate, it is necessary to control the scanning speed of the reticle or the substrate very precisely and stably. Generally, for this purpose, a scanning exposure apparatus is provided with linear motor means which is, as shown in FIG. 14, incorporated into driving means of a scanning stage device for holding and scanningly moving a reticle or a substrate. The illustrated device comprises a base 101, a guide 102 fixed to the base 101 and having a U-shaped sectional shape, and a wafer stage 103 movable reciprocally in a predetermined direction (scan direction) along the guide 102. The device further comprises a pair of linear motor stators 104 and 105 disposed at opposite sides of the movement path of the wafer stage 103, which is movable along the guide 102, and being provided integrally with the base 101. The device further comprises a pair of linear motor movable elements 106 and 107 which are provided integrally with the sides 103a and 103b of the wafer stage 103, respectively. The linear motor stators 104 and 105 and the linear motor movable elements 106 and 107 constitute a pair of linear motors E1 and E2 for providing acceleration and deceleration of the wafer stage 103 in the scan direction. The wafer stage 103 is guided by the guide 102 without contact thereto, through association of static pressure bearing means (not shown), for example.
The linear motor stators 104 and 105 have elongated loop-like yokes 104a and 105a, extending along and substantially throughout the length of the guide 102, and elongated magnets 104b and 105b fixed to the insides of the yokes 104a and 105a, respectively. The magnets 104b and 105b extend through coil openings 106a and 107a, respectively, of the linear motor movable elements 106 and 107, respectively. When the linear motor movable elements 106 and 107 are energized in response to supply of drive currents from a voltage source (not shown), thrust forces are produced along the magnets 104b and 105b by which the wafer stage 103 is accelerated or decelerated.
Wafer W0 is attracted to the wafer stage 103 and, above the wafer, a reticle is held by a reticle stage 203 (see FIG. 17). By means of slit-like exposure light L0 (its section being depicted by a broken line) impinging on a portion of the reticle, a slit-like region of the wafer W0 is exposed such that a portion of the reticle pattern is transferred to that region. Each exposure cycle of the scanning type exposure apparatus comprises moving both the wafer stage 103 and the reticle stage 203 so that the reticle pattern as a whole is transferred to the wafer W0. During movement of the wafer stage 103 which holds the wafer W0, the position thereof is detected by means of a laser interferometer 108 (FIG. 17). The reticle stage 203 has similar driving means such as described above, and it is controlled in a similar way. Speed control during acceleration and deceleration of the wafer stage 103 through the linear motors E1 and E2, is performed in the following manner.
FIG. 15 is a top plan view of the scanning stage device of FIG. 14. When, for example, the wafer stage 103 is at the leftward end position in the scan direction as viewed in the drawing and the center O0 of the width of the wafer W0 in the scan direction is at the acceleration start position P1, acceleration by rightward thrust of the linear motors E1 and E2 as viewed in the drawing starts. Acceleration stops when the center O0 of the wafer W0 comes to the acceleration end position P2. After this, the liner motors E1 and E2 serve only to control and maintain a constant scanning speed of the wafer stage 103. When the center O0 of the wafer W0 comes to the deceleration start position P3, deceleration by leftward thrust of the linear motors E1 and E2 as viewed in the drawing starts. When the center O0 of the wafer W0 comes to the deceleration end position P4, running of the wafer stage 103 stops. Simultaneously therewith, leftward acceleration as viewed in the drawing starts. Moving the wafer stage 103 leftwardly, as viewed in the drawing, is performed by controlling the linear motors E1 and E2 in a similar way but in the opposite direction.
In such an acceleration and deceleration cycle, if for example the wafer stage 103 runs rightwardly as viewed in the drawing, the exposure process starts just when the center O0 of the wafer W0 comes to the acceleration end position P2, such that the exposure light L0 impinges on a rightward end slit-like region of the wafer W0 as viewed in the drawing. When the center O0 of the wafer W0 comes to the deceleration start position P3, the exposure of the whole surface of the wafer W0 is completed. Thus, during exposure of the wafer W0, the wafer stage 103 moves at a constant scanning speed, and the reticle (not shown) moves similarly. The relative position of the wafer W0 and the reticle at the time of starting of the exposure process is controlled precisely, and the speed ratio of the wafer W0 and the reticle is controlled so that it exactly corresponds to the reduction magnification of a projection optical system disposed between the wafer and the reticle. After completion of the exposure process, both the wafer and the reticle are decelerated appropriately.
For a higher productivity of a scanning type exposure apparatus, it is desirable to reduce, as much as possible, the time to be consumed by the acceleration and deceleration of the linear motors E1 and E2. Also, from the viewpoint of saving space, the moving distance of the wafer stage 103 during acceleration and deceleration of the linear motors E1 and E2 should desirably be short. This requires that the linear motors E1 and E2 provide a large thrust and also that the strength of the magnetic field of the linear motor stators 104 and 105 is very large, such as about 5,000 G., for example. In order to meet this requirement, the yokes 104a and 105a may be made of a material such as iron, for example, having a high saturation magnetic flux density, but even on such an occasion it is still necessary that the opposite end portions 104c and 105c (FIG. 16) of the yokes 104a and 105a, where the magnetic flux of the magnetic field is strong such as discussed above is concentrated, have a very large sectional area so as not saturate the concentrated magnetic flux.
In the arrangement described above, the opposite end portions of the yokes of the linear motor stators should have a very large sectional area so as to avoid saturation of the magnetic flux. Additionally, the central portion of the yoke (where acceleration or deceleration of a wafer stage, for example, is not necessary) has the same sectional size of the end portion thereof. As a result, the yoke as a whole has a very large weight. Thus, the device as a whole is very large and very heavy. Also, for producing a large magnetic field as described above, the magnet of the linear motor stator should have a large thickness, and it should be made of a rare earth magnet which is very expensive. If a thick and expensive magnet is provided along the entire running path of the scanning stage, the cost of the linear motor becomes very high.
Further, as shown in FIG. 17, as regards the reticle stage 203, it is necessary that a base 201 thereof is supported by a frame 204 which is integral with the base 101 of the wafer stage 103, and additionally that the reticle stage is accelerated to a speed, four or five times higher than the speed of the wafer stage 103. For this reason, there occurs a problem of vibration of the reticle stage 203 due to the reactive force of the -linear motor. More specifically, since the reticle stage 203 is located in an upper portion of the exposure apparatus, structurally a vibration easily occurs. Also, since the reticle stage is driven by a large drive force as compared with that of the linear motor means of the wafer stage 103, the exposure apparatus as a whole is swingingly vibrated to a great degree which causes a large external disturbance to a servo system of the exposure apparatus. Since such an external disturbance is a bar to synchronization of scanning of the reticle stage 203 and the wafer stage 103, it is necessary to delay the start of the succeeding exposure cycle until the external disturbance diminishes. Thus, the throughput is low.
Furthermore, if the exposure apparatus as a whole is swingingly vibrated, it may cause deformation of the frame 204 which supports the reticle stage 203 and the projection optical system 205, which may result in a large error in detected values of the laser interferometers 108 and 208, for example, for detecting the positions of the wafer stage 103 and the reticle stage 203, respectively.
It is an object of the present invention to provide a solution for at least one of the problems described above.
It is another object of the present invention to provide a stage device by which reduction in size, reduction in weight, reduction in heat generation or reduction of cost is assured.
It is a further object of the present invention to provide an exposure apparatus having such a stage device.
It is a still further object of the present invention to provide a stage device by which vibration due to drive can be reduced considerably.
It is yet a further object of the present invention to provide an exposure apparatus having such a stage device as discussed above.
It is yet a further object of the present invention to provide a device manufacturing method for manufacturing high-precision microdevices by using an exposure apparatus such as described above.
In accordance with an aspect of the present invention, there is provided a stage device, comprising: a movable stage being movable along a path having a constant speed movement region and an acceleration region; first thrust producing means for accelerating and moving said movable stage in said acceleration region of said path; and second thrust producing means, separate from said first thrust producing means, for moving said movable stage at a constant speed in said constant speed movement region of said path.
As compared with the first thrust producing means which provides positive or negative acceleration of the movable stage, the second thrust producing means for moving the movable stage at a constant speed can be made considerably light in weight and small in size. Thus, the driving means portion of the stage device can be small in size, light in weight, low in heat generation and small in cost.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.